• Remove the meat from the refrigerator 30 minutes before smoking.
• Use a sharp knife to trim away excess fat cap from an 8 lbs boneless beef rib roast. Save the fat for other uses. If you have a bone-in roast and want to trim it, stand the roast on it's end, so the cut bones face up and use a sharp boning knife (or carving knife) to cut away the bones in one piece, following their natural curve with the blade.
• Use a 10-12-foot length of kitchen string to tie the roast, hold its shape, and ensure the meat cooks at a uniform rate without grey spots.
• To tie the roast, tuck any loose ends under the meat and position the kitchen string under one end of the roast; tie a snug knot around the end (tied off on top of the meat). Pull the long end of the string about 1-1½" further along and hold it with one finger pressed into the roast. Wrap the loose end around the roast. When you bring it up, tuck it under the piece you're holding with the string and pull it, then alternate tucking the string under and over snugly along the top.
• Continue wrapping, tucking and pulling all the way down the roast until you reach the other end. Flip the meat over and alternate tucking the string under and over the string on the underside to hold it in place. Finally, join the two ends together and tie a snug knot.
• You can tie the ribs back onto the bone to remove just before carving, or reserve them for roasting, smoking or grilling later (they are dinosaur bones and they're delicious).
• Combine 2 tablespoons kosher salt and 1 tablespoon black pepper in a bowl and mix well. Drizzle 1-2 tablespoons olive oil over the roast and spread it over the entire thing (top, bottom and sides). Sprinkle the salt and pepper mixture over the meat, rubbing and pressing it in so it's evenly coated everywhere and the seasoning sticks to the meat.
• In a small bowl combine 2 tablespoons prepared horseradish, ¼ cup Dijon mustard, 2 tablespoons whole grain Dijon mustard, 1 tablespoon fresh thyme and stir to combine.
• Slather the wet rub over the meat, coating every part evenly.
• Heat the smoker to 225°F, and when it is smoking, place the prime rib in the center. If your smoker has a tethered thermometer, insert the probe(s) in the center of the meat for the most accurate reading. Close the lid and smoke for 3-3½ hours, until the internal temperature reaches about 118°-122°F.
• If you're using an instant read, start checking the internal temperature after about 2½ hours to see how far along it is. You don't want to keep opening the lid, as it lowers the smoker's temperature, but you also don't want to let the meat go past your desired doneness.
• Once the meat has achieved the temperature range, transfer it to a platter and tent it with foil to rest.

SEAR THE MEAT:

• As the meat rests, turn up the grill to 500°. When it reaches the target temperature, place the roast on the grill to sear the exterior and achieve a burnished crust. Use heat-proof gloves or tongs to roll the roast, so that each part is touched by the high heat.
• If you have sear plates, arrange them on the smoker and turn the heat up to 500°F. (It usually takes 15-20 minutes to come to temperature). Place the roast on the sear plate and rotate it every minute or so, to crust every part of the roast. Some of the mustard-horseradish coating will adhere to the plate; that's fine.
• Degree doneness by internal temperatures:

  Rare: 130°F; Medium-Rare: 135°F, Medium: 140℉

  Check the readings on your thermometer to ensure it's cooked to your desired temperature.
• Remove the meat to a platter or cutting board with a deep well to collect juices, and set aside for 20-30 minutes to allow the juices to redistribute throughout the flesh.
• After the prime rib roast has rested, use a long, thin carving knife to carve slices into ½-1" slices, depending on appetites. Serve with any jus collected from the smoking process or from the meat as it rested, as well as horseradish or bordelaise sauce.